Pitcher plant description

This spectacular carnivorous plant from Asia grows modified pitcher-shaped leaves, which hang from coiled tendrils, into which insects and other invertebrates fall (2)(4). Nepenthes bongso is a vine climbing to a height of about five metres, with tendrils reaching about 30 centimetres long and pitchers that grow up to 35 centimetres long (2). Nepenthes species usually have two or three different types of pitcher, generally known as upper and lower pitchers (4). These pitchers contain an acidic fluid, secreted by the many glands which cover the inside surface of the lower half of the pitcher (4). In Nepenthes bongso, the lower pitchers are spherical, while the upper pitchers are larger and trumpet shaped (2). The pitchers are green with red lines running down them and the flowers vary in colour from creamy green to red (5). The smooth and waxy upper inner surface of the pitcher makes it impossible for captive insects to gain a foothold (4), and a ridge of hardened tissue lining the mouth of the pitcher, the peristome, bears downward pointing teeth, also preventing insects from escaping. A lid overhanging the mouth of the pitcher prevents rain water from diluting the pitcher fluid (6).

Related species

Pitcher plant biology

Pitcher plants are dioecious, meaning that male and female flowers grow on separate plants (4), and only begin to flower once the upper pitchers are produced (6). The flowers produce large amounts of nectar during the early evening and night, which evaporates by the morning. This nectar attracts flies during the early evening and moths at night to aid pollination. Once fertilised fruits usually take about three months to develop and ripen. Fruits of Nepenthes species usually contain between 100 and 500 very light, winged seeds, which can measure up to 30 millimetres long and are thought to be dispersed by the wind (4)(6). Despite enormous numbers of seeds being produced, only a few manage to germinate and only a fraction of those survive to maturity (6).

Carnivorous pitcher plants are adapted to grow in soils low in nutrients. Although the plants do gain some nutrition through the soil, and energy through photosynthesis, they supplement this with a diet of invertebrates, usually consisting of ants, cockroaches, centipedes, flies and beetles. Insects are attracted to the pitchers by their bright colours and nectar, which is secreted by glands situated on the lid and the peristome of the pitcher. The insects fall into the acidic fluid at the base of the pitcher and, unable to escape, they drown. Digestive enzymes are then released to break down the captured prey (4).

Despite the hostile environment of the pitchers, they can be home to number of animals. The red crab spider (Misumenops nepenthicola) inhabits pitcher plants in Malaysia, Indonesia and Singapore. This spider ambushes insects that crawl into the pitcher, and preys upon other insects, such as mosquitoes, as they emerge from larvae that live in the pitcher fluid (6).

Pitcher plant status

Pitcher plant threats

Nepenthes species are threatened by a combination of over-collection and habitat loss (6). Montane forest only covers eight percent of Sumatra and the highly restricted range of Nepenthes bongso makes it particularly susceptible to the impacts of habitat disturbance or catastrophic environmental events such as drought and fire. In addition, highland plants, such as Nepenthes bongso, take longer to recover from any disturbance than lowland plants, as growth is slower (2)(6).

Pitcher plant conservation

Although listed under Appendix II on the Convention on International Trade in Endangered Species (CITES) which limits the international export of this species (3), trade is very difficult to regulate. There is no requirement for internationally traded Nepenthes to be identified down to species level and plants simply labelled as Nepenthes accounted for 94 percent of all exported Nepenthes plants between 1988 and 1993. This needs to be remedied and urgent attention is required to close other trade loopholes (6). Nepenthes bongso tends to occur in remote or protected locations resulting in less collecting than some other Nepenthes species and is relatively easily cultivated helping to reduce the impact on wild populations (2).

Glossary

A species or taxonomic group that is only found in one particular country or geographic area.

Enzymes

Proteins that trigger, or accelerate, activity in the cells of the body, for example, breaking down foods during digestion, and building new proteins..

Epiphyte

A plant that uses another plant, typically a tree, for its physical support, but which does not draw nourishment from it.

Fertilisation

In a flowering plant, fertilisation is the process of a pollen grain joining with the ovule (female egg cell). After fertilisation, the female parts of the flower develop into a fruit.

Inflorescence

The shoot of a plant which bear a group or cluster of flowers.

Invertebrates

Animals with no backbone.

Larvae

Stage in an animal’s lifecycle after it hatches from the egg. Larvae are typically very different in appearance to adults; they are able to feed and move around but usually are unable to reproduce.

Montane forest

Forest occurring in the montane zone, a zone of cool upland slopes below the tree line dominated by large evergreen trees.

Photosynthesis

Metabolic process characteristic of plants in which carbon dioxide is broken down, using energy from sunlight absorbed by the green pigment chlorophyll. Organic compounds are made and oxygen is given off as a by-product.

Pollination

The transfer of pollen grains from the stamen (male part of a flower) to the stigma (female part of a flower) of a flowering plant. This usually leads to fertilisation, the development of seeds and, eventually, a new plant.

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